1610 was the last year of Caravaggio's life. In that final year, he painted "The Denial of Saint Peter." The painting usually hangs at the Metropolitan Museum of Art in New York City. Right now it is in Los Angeles, at LACMA for a show called "Bodies and Shadows: Caravaggio and His Legacy." It is not the featured painting of the show. It is not, even, a painting that your typical Caravaggio lover would be expected to love. It is darker than most of the more famous Caravaggios, murky even. It doesn't have the disturbing imagery or the intense physical luminescence of a painting like "Judith Beheading Holofernes." You could call it a subtle painting, from a painter not usually singled out for his subtlety.

The painting is a scene from the Gospels. On the day that Jesus is to be arrested, he tells the Apostle Peter that Peter will deny him three times before the next morning. Peter swears this is impossible. Soon after, Jesus is betrayed by Judas and taken by the authorities. The apostles have scattered in fear and confusion. A servant girl points Peter out among the crowd and tries to expose him as also a follower of Jesus. No, no, Peter says, you have got the wrong fellow. Peter is worried for his own life now. As foretold, Peter goes on, three times, to deny any relationship to Jesus.

This is the moment that Caravaggio captures in his painting. The servant girl, the accuser, stands in the middle of the painting, just off to the left, next to a soldier brought, presumably, to arrest Peter. Peter stands at the right of the painting, facing slightly toward the viewer. His hands are turned in toward his own body, gesturing at himself in his act of denial. Light from an unseen source somewhere to the left of the painting shines strongly on Peter's forehead. The soldier is in shadow; his face can barely be seen. The servant girl is partially blocked from the light by the body of the soldier, but a strip of the same light that is falling upon Peter catches her squarely in the eyes. The painting seems to be a straightforward illustration of this biblical scene at a crucial moment. Will Peter be exposed? Will he admit who he really is?

In fact, the painting is not so straightforward as all that. And we can thank the great contemporary art critic Michael Fried for helping us to see the complexity that undergirds all of Caravaggio's paintings. Fried published a book in 2010 called The Moment of Caravaggio. It is a book of bold ideas. You can't look at Caravaggio the same way after reading Fried. Today, in the early 21st century, Caravaggio has become Fried's Caravaggio. This is appropriate, since much of what Fried says about Caravaggio simply must be true. It is true that Caravaggio's paintings are "immersive," as Fried puts it. The viewer easily becomes immersed in the paintings, and the figures in the paintings are, themselves, often portrayed as immersed in whatever they are doing. Throughout Caravaggio's painting can be found the quality of "intensely imagined inwardness." And yet, this is an inwardness that is presented to the viewer in the form of a painting. We are meant to be spectators of the immersion. These two aspects of Caravaggio's paintings, the "immersive" and the "specular" aspects, as Fried calls them, vie with one another in all of Caravaggio's most striking canvases.

According to Michael Fried, Caravaggio's paintings contain complicated arrangements of looking and being looked-at. Because of this, the figures depicted in Caravaggio's paintings are not always looking where they might be expected to look. Take, again, "The Denial of Saint Peter."

An act of recognition is happening here. But whose recognition, and for what? The soldier is completely in the dark, literally and figuratively. He is simply following orders, trying to arrest the people who are supposed to be arrested. Peter is the most important figure in the painting in that he is the historical and narrative protagonist. The painting is about him, about his act of denial. Peter is trying desperately, in the painting, not to be recognized. He isn't looking at the servant woman. He is barely looking at the soldier. He is trying not to look like himself and his face reveals the difficult and somewhat comical nature of such a task. He doesn't really know where to look. His eyes are trying to wander away. Peter wants to look confused and he wants the soldier to be confused by his own confusion. In this, he will be successful. According to the Gospels, Peter is not arrested.

The servant girl has failed. She meant to convince the soldier that Peter was a follower of Jesus. She is not able to do so. Maybe she herself has doubts. She thinks she saw Peter with Jesus, but maybe not. In a painting of this crucial and dramatic scene, the servant girl ought to be looking intently at Peter, trying to figure out whether this is really the man. You would also think that Caravaggio would portray the servant girl as indecisive, or as otherwise unpersuasive. But that is not how she looks. In fact, she isn't looking at Peter at all. She seems, at first glance, to be looking at the soldier. But look closely at her eyes, look at her face. She is, actually, the central figure of the painting and not because of anything directly to do with Peter. Something is happening to her and to her alone.

The servant girl is not looking at the soldier either, even though she is turned in his direction. Her attention has been captured by something else. Look especially at the way that her right eye has drifted from the action. Peter is standing right behind her, engaged in his act of denial. But the servant girl has, internally, gone away from this scene. She isn't looking at Peter; she isn't looking at the soldier. What is she looking at? She came to this spot trying to recognize Peter. Instead, she has recognized something about herself. The servant girl is seeing herself anew; she is seeing herself transformed.

I sometimes wonder if the most important single influence on painting in the 16th and 17th centuries is the Council of Trent. In the mid-16th century, the high and mighty of the Catholic Church took up a nearly impossible task. They were going to respond to the challenge of the Protestant Reformation without actually admitting that the challenges of the Protestant Reformation were valid. The point of the Council was to reform the Church without changing it too much, to refute all criticism of the Church while, simultaneously, enacting internal reforms in response to some of those same criticisms. Tricky business. No wonder it went on for nearly two decades. One of the edicts of the council had a direct bearing on the making of art. Art had become a subject of theological debate in the 16th century since many Protestant reformers had begun openly to condemn art that included sacred images. These images were seen as a violation of the second commandment, which prohibits the creation of graven images. For Protestants, the adoration of a painting of, say, the Virgin Mary, was akin to idol worship. The Catholic Church, at the conclusion of the Council of Trent, responded with a document called "On The Invocation and Veneration of Saints, on the Holy Relics, and on Sacred Images." This document pronounced religious art to be, on the whole, good and helpful for proper holy behavior. After the Council of Trent, a number of influential Church theologians elaborated further on the nature of religious art. The overriding emphasis was on the necessity for religious art — painting in particular — to come from real emotion and feeling and to convey real emotion and feeling. At the core of this was the old Catholic love of the mystery of faith. You cannot, so the thinking goes, reason yourself into belief. Belief comes first, and it comes, often enough, like a shot from the blue. A person is transformed in the process of conversion without ever fully understanding what has happened. Pascal described his experience of conversion on the night of November 23rd, 1654 like this: "From about half-past ten in the evening until about half-past twelve … FIRE … God of Abraham, the God of Isaac, the God of Jacob, and not of the philosophers and savants. Certitude. Certitude. Feeling. Joy. Peace." Fire in the night and then a reorientation of all the things you know and feel. It happened to Paul on the road to Damascus.

It happened as well, so Caravaggio tells us, to the servant woman as she was in the process of exposing Peter to the authorities. Caravaggio's "The Denial of Peter" is a Council of Trent painting. And it is intriguing to consider the formal structures of immersion and specularity that Michael Fried so convincingly shows Caravaggio to have discovered as techniques used in the service of a greater purpose. Caravaggio was not interested in immersion and specularity as such — he was interested in painterly devices that would help him portray the mystery of faith. Given Caravaggio's own complicated life — his crimes, his brutality, his notorious act of murder — it is, perhaps, not so surprising that Caravaggio would be such a tremendous Counter Reformation painter. Counter Reformation theologians were fond of quoting a line from Horace, which reads, "If you want me to weep, weep yourself." The servant girl in the Gospel stories is up to no good. She is a troublemaker, stirring up trouble for Peter simply because she can. Maybe she will benefit from doing so, maybe not. But she can't resist the opportunity to create mischief for mischief's sake. And then something happens to her. She is turned inward, transformed, never to be the same again. The transformation on the face of the servant girl is something akin to the transformation that Caravaggio brought to the history of painting. He turned painting in a different direction. He converted it. • 2 January 2013